The magnetic tunnel junction (MTJ), one of the most prominent spintronic devices, has been widely utilized for memory and computation systems. Electrical writing is considered as a practical method to enhance the performance of MTJs with high circuit integration density and ultralow-power consumption. Meanwhile, a large tunneling magnetoresistance (TMR), especially at the non-equilibrium state, is desirable for the improvement of the sensitivity and stability of MTJ devices. However, achieving both aspects efficiently is still challenging. Here, we propose a two-dimensional (2D) MTJ of 1T-MnSe2/h-BN/1T-MnSe2/h-BN/1T-MnSe2 with efficient electrical writing, reliable reading operations and high potential to work at room temperature. First, for this proposed MTJ with a symmetrical structure and an antiparallel magnetic state, the degeneracy of the energy could be broken by an electric field, resulting in a 180° magnetization reversal. A first principles study confirms that the magnetization of the center 1T-MnSe2 layer could be reversed by changing the direction of the electric field, when the magnetic configurations of the two outer 1T-MnSe2 layers are fixed in the antiparallel state. Furthermore, we report a theoretical spin-related transport investigation of the MTJ at the non-equilibrium state. Thanks to the half-metallicity of 1T-MnSe2, TMR ratios reach very satisfactory values of 2.56 × 103% with the magnetization information written by an electric field at room temperature. In addition, the performance of the TMR effect exhibits good stability even when the bias voltage increases gradually. Our theoretical findings show that this proposed MTJ is a promising high performance spintronic device and could promote the design of ultralow-power spintronic devices.